Section 3
Acidic and Basic Solutions
Acidic and Basic Solutions
Acids
• Acids are substances that release positively
charged hydrogen ions, H+, in the water.
• H+ will combine with water releasing a
positively charged ion called hydronium (H3O)+
HCl + H2O -----> (H3O)+ + Cl-
Acidic and Basic Solutions
3
Bases
• Bases are substances that release negatively
charged hydroxide ions, OH-, in the water.
• NaOH +H2O ---------> Na+ + OH- + H2O
Acidic and Basic Solutions
Strengths of Acids and Bases
• The strength of an acid depends on how
easily the acid will release H+ (hydrogen)
ions when in water
• The strength of a base depends on how
easily the base will release OH- (hydroxide)
ions when in water
pH
pH is a measure of how acidic or basic a
solution is and depends on the concentration
of hydronium and hydroxide ions.
pH can be measured.
Mini Lab 1: testing
substances with Litmus
paper
Litmus paper
Red
Blue
Acid or Base?
Ammonia
Turn blue
Stay blue
base
Soda
Stay red
Turn red
acid
*Litmus paper
Litmus paper turns red or stay red when in contact
with an acid
Litmus paper turns blue or stay blue when in
contact with a base
Acidic and Basic Solutions
Indicators
• Indicators are compounds that react with
acidic and basic solutions and produce
certain colors, depending on the
solution’s pH.
• Indicators help you determine the pH of a
solution.
• There are several types: litmus paper and
universal indicator are examples
Universal Indicator – gives you different colors
according to the pH of the solution
Universal Indicators have a pH scale.
To use it, you dip the paper in the solution to be tested
for pH and compare the
color on the paper with
the color on the scale.
When you find the
matching color you
have the pH of the
solution.
pH and pH Scale
pH is a measure of how acidic or basic a
solution is and depends on the concentration
of hydronium and hydroxide ions present in the
solution.
pH scale is a scale that shows the different pH values
pH Scale - ranges from 0 to 14
•
•
•
•
Acidic solutions have pH values below 7.
A solution with a pH of 0 is very acidic.
A solution with a pH of 7 is neutral.
Basic solutions have pH values above 7.
Acidic and Basic Solutions
*Properties of Acidic Solutions
-sour taste
-can conduct electricity because it has ions
-are corrosive, which means they break down
certain substances. Many acids can corrode
fabric, skin, and paper.
-react strongly with certain metals.
Ex: vinegar, sulfuric acid, citric acid ( in
oranges, lemons…)
Acidic and Basic Solutions
Properties of Basic Solutions
Slippery
Bitter taste
Bases are corrosive.
Bases can conduct electricity ( have ions)
Basic solutions are not as reactive with metals
as acidic solutions are.
Ex: ammonia, soaps, blood
Examples of Acids and Bases
See table on the book page 639.
Acidic and Basic Solutions
Neutralization
*Neutralization is the reaction of an acid
with a base. Ex:
It is a chemical reaction because new
substances are being formed ( salt and water)
Acidic and Basic Solutions
*How does neutralization occur?
The reaction of a base and an acid results in
water and a salt (always!!!). Water and salt have
neutral pHs.
This reaction is called neutralization because the
acid and the base are not there anymore, so the pH
of the new solution is neutral.
HCl + NaOH  NaCl (neutral) + H20 (neutral)